Upgrade from TeX Live 2017 to 2018

That is, you should have a specific reason to do an upgrade
instead of a new install, and you should be familiar with Unix and TeX
Live. If you have any doubts whatsoever, please do a new installation.

We do not provide a dedicated upgrade script. The procedure here is
not bullet-proof, or recommended; consider it provided as-is, to be used
at your own risk, if you want to do so, for reasons of your own. It's
your responsibility to understand what is being done. Failing any of
that, please do a new installation.

These instructions say nothing about what is done as root or as a
normal user; that's because TeX Live installations are done both ways
(root is not required for anything in TL itself), and we can't know
which you chose. You need to know. If you don't, do a new
installation.

It's not possible to upgrade to TL'18 from TL'15 or earlier.

Unix

Find the parent directory of the current installation; it's
/usr/local/texlive by default.

To save some space, you can exclude tlpkg/backups/* or
remove them from the 2018/ directory afterwards.
(Theoretically, you could rename 2017 to 2018,
but we strongly advise against this, since you may lose your
existing installation with no good way back.)

If you installed symlinks in system directories (via the installer
option or tlmgr path add), remove them now with
tlmgr path remove.

As needed, adjust your PATH in your startup files to
point to .../2018/bin/platform instead of
.../2017/....

Log out and log in, and confirm that your PATH now has
the 2018 directory. This is crucial. Your PATH must use the
new location.

cd to your top-level .../2018 directory.

Download the latest update-tlmgr-latest.sh and run it like this:
sh update-tlmgr-latest.sh -- --upgrade(The extra options are to try to prevent the upgrade from
happening unintentionally.)

If you don't want to use the default repository (that is, not the
automatic CTAN redirection) for downloading the new files, run (as usual):
tlmgr option repository yourrepo

Run (with patience, it will be downloading all the new material):
tlmgr update --self --all

Remake the lualatex/fontspec cache:
luaotfload-tool -fu

If you want symlinks in system directories (not recommended),
run tlmgr path add.

When you are happy with how the new TL is working, if you wish
you can remove the old installation by running .../2017/.../tlmgr
uninstall (full tlmgr doc). Not
recommended, since you might always find a document that doesn't work
with the new version, just at the wrong time …

Good luck, and to reiterate from the top, don't do any of this if it
doesn't make sense to you. Just do a fresh installation.

Windows

There is no comparable upgrade procedure for Windows. Doing a
new installation is necessary.